The objective of this study is to investigate the feasibility of the surface-replacement concept of hip arthroplasty in conjunction with various types of fixation methods. Current clinical investigations of surface replacement designs use either press-fit components or acrylic cements for fixation. In this study, these two types of designs will be compared with a third, using bone-ingrowth as the method of fixation for the femoral cup, the acetabular sockets being cemented in every case. The aim is to determine whether the bone-ingrowth fixation method and the surface-replacement concept represent a viable and perhaps optimal form of total hip replacement. The experimental in-vivo model will consist of 60 adult, mixed German Shepherd dogs, carefully screened for disease and selected on a basis of size and weight parameters. Care has been taken to document the epistemology of each aspect of this program, which necessarily covers a wide range of topics, varying from clinical studies of cup arthroplasties to mechanical testing of new fixation concepts. The results of the one to eighteen months' canine follow-up regime incorporated in the three-year program, will be analyzed by various related techniques, including clinical and radiographic, bone-scanning SEM and light microscopy of the sections, histopathological, microradiographic and mechanical studies.